Water is employed in a wide range of industrial processes and for a wide range of purposes, each of which imposes its own requirements or characteristics on the properties of the water entering and discharged by the process. Such requirements on the properties or characteristics of water used in or discharges from various processes in turn often result in water treatment processes necessary to make the water suitable or acceptable for use in or discharge from the process, and the various water treatment processes in themselves may be a major technical or economic component of an industrial process.
Various industrial processes can impose a number of chemical and physical requirements on incoming water, such as acidity, salinity, temperature and so on, and corresponding requirements on discharge water, typically to meet environmental or health requirements. In many commonly found industrial processes, however, the principle requirements for input and discharge water concern the particulate or suspended contents of the water rather than, for example, the dissolved contents of the water.
Examples of processes in which the particulate or suspended contents of the intake and discharge water are the primary concern are found in the stone fabrication industry, such as those involved in cutting, shaping and polishing natural, engineered and man-made stone for such products as countertops, flooring, architectural paneling, and so on. As is well known by those of ordinary skill in these arts, water is commonly used to wash away the particulate waste material from the cutting and polishing processes, as a coolant to carry off heat produced by the processes, and often as a lubricant. As a consequence, stone cutting and polishing processes, whether of natural stone, engineered stone or man-made stone-like materials, generate heat and significant volumes of particulate waste material, both of which are carried away in and by the process discharge water. The discharge water is consequently referred to as “grey” water, because of the particulate waste material in the water. The particulate waste material is primarily comprised of the material being cut or polished, but will often include other particulate material, such as particles from the cutting and polishing tools themselves, polishing or cutting compounds used with the tools and processes, and various other materials that find their way onto the floor and into the waste water system.
The type and degree of treatment performed on the grey discharge water from the processes depends, in turn, on what is done with the discharge water. For example, the grey water that is eventually discharged from the processes and the treatment of the grey water before final discharge may be dictated by environmental or health factors. In some instances, the grey water may be treated in no more than a “settling tank” to allow at least some of the particulate waste to “settle out” as sediment before the water is returned, for example, to a river or discharged to enter the groundwater. In addition, water discharged into rivers, streams, groundwater and so on is required to meet state and federal requirements, which typically require ongoing random testing of the discharged water in compliance with the Clean Water Act. In most instances, environmental or health concerns may require removal of the particulate waste to the level of “crystal clear” water, as discussed below, as well as other MCL (maximum containment level) measurements before it is returned to the environment or original source.
In still other instances, at least some of the grey water may be recycled to the processes as intake water, thereby reducing the total water volume requirements of the processes. The treatment of recycled grey water will depend, however, upon the uses to which the grey water is to be put. For example, certain processes, and in particular stone cutting, drilling and cooling processes, may use grey water containing a moderate amount of particulate waste as the particulate waste from a previous cycle through a stone cutting or polishing and Computer Numeric Controlled (CNC) process may not adversely affect a cutting, drilling, cooling or coarse grinding process. In such instances, the recycled grey water may require no more than a settling tank to allow sedimentation of enough of the particulate waste material that the remaining waste material in the grey water does not “clog” the ensuing process in which it is used, or may require no treatment at all.
In other instances, however, the process or processes receiving recycled water require “crystal clear” water, that is, water in which the volume and size of particulate matter is strictly limited. Stone polishing, CNC processes and water jets, for example, must use intake water that is “clear”, that is, water that generally contains no particulate matter, except particles that are generally less than 1 or 2 microns in diameter, as larger particulate matter will interfere with the polishing or CNC process by making and leaving scratches that will prevent the desired degree of polish or finish, that may leave visible scratches and that may clog the polishing tools, CNC spindle and water jets.
The recycling of grey water into “clear” water, however, is a technically and economically more complex and expensive process than a sedimentation tank as used to recycle grey discharged water to grey intake water for such processes as cutting, drilling, cooling and coarse grinding, and the choice is subject to many factors. For example, it may be less expensive to provide fresh intake water for those processes requiring “clear” water, and to treat all discharge water as grey water for both discharge and recycling purposes. In the alternative, however, and very often, the required quantities of fresh intake water, or intake water of sufficient quality, may not be available or may be more costly than cleaning and recycling grey water into crystal clear water, or the volume of grey water that may be discharged may be limited for any of a number of reasons.
The problem, therefore, is to provide an environmentally sound water recycling system for industrial processes such as stone cutting, grinding, cooling, polishing and for CNC equipment and water jets that virtually eliminate the required volume of fresh intake water and absolutely eliminates all grey discharge water from a facility, by economic and efficient recycling of grey water into crystal clear water and grey water in the required quantities.
It will be seen from the following descriptions of the present invention that the general methods for removing particulate matter from grey water to provide clear water or a combination of clear water and filtered grey water for various purposes is not a straightforward process but contains many inherent problems that must be addressed in addressing the basic problem.
For example, the general methods for the removal of particulate matter such as stone residue from a fluid such as water typically include settlement, which may also be referred to as sedimentation, and filtering. Sedimentation essentially employs the differences in density between the fluid and the particulate matter to separate one from the other and, which is usually relatively inexpensive, is relatively slow and is less effective as the particle size decreases. Also, while the sedimentation rate and particle separation capacities of a sedimentation system may be enhanced by, for example, chemical methods, these enhanced methods are much more expensive and typically provide questionable recycled water quality and volumes.
Filtering methods pass the water and particulate matter through some form of trap, clarifier centrifuge or other media that will capture the particles but will pass the water and typically are faster but much more expensive than simple sedimentation methods. For example, the “high pressure filter”, or filter press, was originally designed to “dewater” solids that had settled in a collection tank or basin, that is, the particulate matter collected in a sedimentation tank in an industrial wastewater treatment environment. In this process, waste water bearing the waste particulate matter from an industrial process was allowed to stand in a sedimentation collecting tank to allow at least a part of the particulate matter to settle out of the water, often with the use of a chemical precipitant. The particulate sediment settled out in the sedimentation tank, which contained a significant proportion of water, and was pumped to the filter press, which essentially removed the water from the sediment by trapping the sediment in the filter press and allowing the recovered water, also referred to as effluent or filtrate, to return to the treatment system. The particulate waste collected in the filters of the filter press was then mechanically removed from the filters of the filter press and was typically discarded.
A filter press of the prior art is therefore effective for removing water from sedimented particulate matter. When employed to remove particulate matter from water, however, which is an object of the present invention and discussed in the following descriptions of the present invention, filter presses have certain disadvantageous limitations. These limitations become particularly obvious when relatively higher volumes of filtered water per unit are required, such as filtered water flow rates up to 150 gallons per minute (gpm) utilizing a single 20 cubic foot filter press.
Stated briefly, the fluid dynamics within a filter press, when combined with the progressive accumulation of solids during the filtering process, prevents a typical 20 cubic foot filter press with an industry standard air actuated, double diaphragm air pump, from producing filtered water at a consistent, reliable, predictable flow rate when the flow rate demanded of the filter press reaches up to 150 gpm.
It has been found, for example, that for a number of reasons standard, industry available filter press components and air diaphragm pumps will not permit the desired yield to be maintained at flow rates of 75 gpm and greater for filter presses having internal filter element volumes higher than a 20 cubic foot filter capacity with filter plates that measure approximately 800-1,000 mm in diameter. For example, in water filtration and recycling systems for stone fabrication shops the type and quantity of particulate solids that are generated during stone processing can result in “slumping” of the accumulated particulate solids in the filter plate voids if the accumulated weight or vertical loading of the particulate solids in the filter elements exceeds a given limit. Once slumping occurs, the filter cloths begin to foul, that is, become clogged with particulate matter as the “precoat” has been mostly removed and the cloth media exposed. The flow rate of the filter press will thereby decrease unacceptably and much sooner than the capacity of the filter press would indicate. The total solids capacity of the filter press will therefore not be achieved. The point at which slumping becomes a significant problem depends on the volume capacity of the filter press and the diameter of the filter plates, and it has been found that the practical upper limit on filter press filter capacity is approximately 20 cubic feet and the practical upper limit on filter plate size is in the range of 800-1,000 mm.
It must also be noted that this problem cannot be alleviated or delayed by reducing the size, that is, the diameter, of the filter plates, because the length of the filter press, that is, the number of plates in the filter plate stack, must therefore be increased to maintain the desired flow rate through the filter press. The increase in the number of filter plates in turn increases the length of the flow path through the filter press and the weight, that is, the size and density, of the particles is typically such that the particles may not be carried through to the last several filter plates at normal flow rates. The particles will therefore tend to accumulate in the first several filter plates, which will then become full faster than would occur with larger plates, and the last several filter plates will tend to accumulate little waste. The clogging of the first several filter plates may cause the flow rate of the filter press to decrease much sooner than would be indicated by the filter volume of the press, and the total solids capacity of the filter press will not be achieved.
It will be recognized, therefore, that these limitations on the capacity and flow rate of filter presses are a significant problem in larger stone processing shops wherein the required clean water flow volumes may reach, for example, up to 150 gpm and beyond.
It must also be recognized that while a filter press will typically be periodically cleaned at scheduled intervals, that is, the filter plates emptied of solids, it is necessary for the system to maintain at least a desired minimum filtered water flow rate over the entire period between filter press cleanings. The minimum desired flow rate, however, will typically be the flow rate normally required by the stone processing equipment in normal operation and may again reach up to 150 gpm per 20 cubic foot press. The flow rate capacity of the filter press will decrease over time, however, because of the accumulation of solids in the filter plates. As a consequence, the actual flow rate that must be achievable at all times may be significantly greater than the desired minimum flow rate.
The present invention addresses and provides a solution for these and other related problems of the prior art.